1. Field of the Invention
This invention relates generally to improvements in cylinder lock and key assemblies and, more particularly, to tumbler pin and key bitting surface designs and to hierarchical lock and key systems.
2. Description of the Prior Art
Yale type cylinder locks are well known and have been in continuous use since 1865. In such locks, key differs are usually developed by adjusting the lengths of a set tumbler pins and the corresponding bitting depths on a corresponding key.
Typically, the tips of the tumbler pins which contact the key bittings are frustoconical or chisel pointed. Examples of such known tumbler pin tip configurations are seen in U.S. Pat. No. 4,289,002 (Gretler), U.S. Pat. No. 4,325,241 (Keller), U.S. Pat. No. 4,760,722 (Fann et al.), and U.S. Pat. No. 5,176,015 (Sussina).
Other variations in the shapes of tumbler tips are also known in the art. For example, U.S. Pat. No. 420,174 (Taylor) shows a master-key lock wherein the lower ends of the lower pins 12 are provided with two dissimilar operative surfaces, which are adapted to be engaged by different keys, creating a master-key system. Similar tumbler pin tip variations are also seen in U.S. Pat. No. 588,026 (Stadtmuller), U.S. Pat. No. 480,299 (Voight), and U.S. Pat. No. 484,443 (Mouat et al.). As another example, U.S. Pat. No. 917,365 (Schoeil) shows a security lock wherein tumbler pins are provided in coaxial pairs and wherein a special key is provided which is capable of moving both pins of the coaxial pair in order to raise the pins to their appropriate height. In particular, by inserting the proper key, the upper bittings 12 enter slots 11 and engage the lower ends of the inner pins 6, while the lower bittings 14 engage the lower ends of the outer pins 5.
Pin tips and corresponding keys are also known which are shaped to adjust the position of the tumbler pin during insertion of the key into the lock. For example, U.S. Pat. No. 3,499,302 (Spain et al.) shows tumbler pins with chisel-shaped tips which are rotatable to predetermined positions by skew cut key bittings to operate in conjunction with a side bar mechanism. In addition, U.S. Pat. No. 4,450,699 (Genakis) shows a tumbler pin having a groove 32' which engages a skewed key ridge 62. These patents show is locks wherein the tumbler pins are adjusted rotationally in addition to the traditional elevational positioning. More recently in U.S. Pat. No. 4,635,455 (Oliver), the tip of a chisel-pointed tumbler pin has been offset, increasing the theoretical bitting and combination possibilities of a six-pin tumbler cylinder.
In addition, a number of techniques have been developed to arrange lock cylinders and their associated keys in hierarchical systems. U.S. Pat. No. 369,628 (Van Hoevenbergh) illustrates segmented pin tumblers disposed in one or more columns which allow several keys which are bitted differently from each other to operate a single cylinder. U.S. Pat. No. 420,174 (Taylor), discussed above, discloses non-rotatable pins with contact key bitting surfaces of different heights to permit different keys to operate the same cylinder. U.S. Pat. No. 564,803 (Stadtmuller) discloses tumbler pins having dual vertical key contact surfaces operable by different keys. U.S. Pat. No. 567,305 (Donovan) provides master keying capability through variations in the shape of the key profile and the corresponding keyway in the cylinder. U.S. Pat. No. 567,624 (Taylor) provides keying capability by using plate tumblers for changing the tumbler-key contact area which allows different keys to operate the same cylinder. In addition, U.S. Pat. No. 3,349,587 (Keller) discloses a method of positional master keying. Cylinders also have been constructed which cooperate with different keys to allow for selective rotation of the barrels. See, for example, U.S. Pat. No. 4,107,966 (Schlage) which discloses a cylinder that is partially operated by one key to retract a latchbolt, and is fully operated by another key to retract the latchbolt and a deadbolt. Some lock systems include interchangeable core cylinders which are operable by a control key, permitting a quick exchange of the core containing the tumblers for a core operated by a different key. See also the prior art classified in class 70, subclass 369 in the U.S. Patent and Trademark Office. Further, some lock cylinders are operable by a first key, but are adjusted when operated by a second key so as to render the cylinders operable only by the second key. See U.S. Pat. No. 3,099,151 (Schlage) and the prior art classified in class 70, subclass 383 in the U.S. Patent and Trademark Office. The above-mentioned patents are only some examples of cylinders that are operable with different keys.
Despite the many hierarchical lock systems known in the art, there remains a need for new and improved lock cylinders that can be operated by more than one key. For example, in large buildings and institutions, cylinders and keys are often arranged in master-keyed systems for the convenience of management personnel.
The positioning of tumbler pins by unique keys has been the subject of continuous improvement in the lock art. Patents issued for the great majority of lock cylinders now on the market have expired. Their keys can be copied on conventional machines of the type described in U.S. Pat. No. 1,439,382 (Segal). The key blanks required are widely distributed beyond the control of the lock manufacturer. The development of skew cut bittings, e.g. Spain et al. discussed above, provided additional security to the key owner because conventional rotary machines could not duplicate these angled cuts. However, because there have been machines developed to duplicate skew cut bittings, their security has been reduced. Uniquely shaped bittings and controlled distribution of proprietary key blanks reduce the odds that keys in the possession of dishonest employees, etc., can be copied at hardware stores and the like.
Notwithstanding existing improvements in the well-worked lock arts, there remains a need for lock systems which provide a large number of unique keys which are not subject to unauthorized duplication. There is also a need for lock mechanisms which resist contemporary lock picking techniques, such as impressioning methods to obtain false keys. It is also desirable that the dimensions of the lock not exceed conventional cylinder size. It is equally important that the components can be economically mass produced.